1. Field of the Invention
The present invention relates generally to medical devices and, more particularly, the invention relates to a filter device that is adapted to capture and remove particles from a body lumen.
2. Description of the Related Art
Vascular filters are used in a wide variety of applications wherein it is desirable to capture particles from the blood. One primary use of vascular filters is for protecting against a condition called pulmonary embolism (PE). A pulmonary embolism occurs when a blood clot (embolus) or other particle in the cardio-pulmonary blood circulation creates a pulmonary arterial blockage. A pulmonary embolism can be a life-threatening condition because the clot may effectively cut off the body's oxygen supply. To reduce the likelihood of this event, a vascular filter may be implanted within a blood vessel, such as the inferior vena cava or other large vein, for capturing blood clots before they can reach the pulmonary vasculature. The use of vascular filters has been particularly useful for treating patients suffering from deep vein thrombosis (DVT), a condition wherein a blood clot (thrombus) can form in a leg and then break free (now an embolus) and migrate into the cardio-pulmonary vasculature.
Delivery of a vascular filter to a blood vessel is usually achieved through a peripheral vein access site, such as, for example, the jugular or femoral veins. One of the earliest examples of a vascular filter is the Mobin-Uddin (“MU”) umbrella filter, which was developed in 1967. The MU filter provided an alternative to a variety of treatment techniques, such as surgical ligation, caval plication, and caval clips, which were used at the time for treating venous stasis and preventing PE. The MU filter is composed of six flat Elgiloy spokes radiating from a hub and partially covered by a web designed to capture blood clots. MU filters were typically introduced into the body via a cutdown of the jugular or femoral vein and subsequent passing of a catheter through the access site to the filter implant site in the infrarenal inferior vena cava.
In 1973, Greenfield et al. introduced a new stainless steel filter. This type of filter is conical in shape and is composed of six equally spaced stainless steel wires. The filter is adapted to hold a clot in the infrarenal vena cava until the body's own lytic system dissolves the clot. Since the introduction of the original Greenfield filter, subsequent derivatives have been developed to reduce the size of the introducer catheter for facilitating percutaneous introduction. For example, in 1989, the Titanium Greenfield Filter (TGF) was introduced as a low-profile system to facilitate the ease of percutanous insertion.
Still other vena cava filters were introduced in the United States in the late 1980s, including the Vena Tech-LGM vena cava filter, the Bird's Nest vena cava filter, and the Simon-Nitinol vena cava filter. The Vena Tech-LGM filter is a conical filter made from a Phynox alloy, with longitudinal stabilizing legs in addition to the intraluminal cone. The Bird's Nest filter is a “nest” of stainless steel wire which is wound into the vena cava, while the Simon Nitinol filter is a two-stage filter made from nickel-titanium (NiTi) alloy with a conical lower section and a petal-shaped upper section. The TrapEase filter is yet another filter that was approved by the FDA in the summer of 2000. The TrapEase filter is laser cut from a single tube of nitinol material and is formed with a symmetric double-basket configuration providing two levels of clot trapping.
Although vascular filters are widely used for capturing emboli in blood vessels, existing filter configurations suffer from a variety of shortcomings that limit their effectiveness. In one primary shortcoming, vascular filters are susceptible to clogging with embolic material. When a filter becomes partially or totally clogged, the flow of blood through the vessel may be substantially reduced or stopped completely. When this occurs, serious complications can arise and therefore the patient must be treated immediately to restore adequate blood flow. Because of the potential for clogging, existing vascular filters are typically manufactured with relatively large pores or gaps such that only large emboli, such as those with diameters of 7 mm or greater, are captured. The large pore size is necessary for reducing the likelihood of clogging due to smaller particles. Unfortunately, in certain cases, the passage of smaller emboli may still be capable of causing a pulmonary embolism or stroke. Accordingly, physicians and filter manufacturers are required to balance the risk of clogging against the risk of pulmonary embolism and/or stroke.
Catheter-based mechanical thrombectomy devices provide an alternative treatment method for removing blood clots from a patient's vasculature. Thrombectomy devices are typically used for removing a thrombus that has formed in a blood vessel and has occluded the flow of blood. Existing thrombectomy devices include the Oasis™ Thrombectomy System by Boston Scientific, the Hydrolyser™ by Cordis, the Helix™ Clot Buster™ by ev3/Microvena, the Arrow Trerotola PTD™ kit by Arrow International, the MTI-Cragg Brush™ by MicroTherapeutics, the Angiojet Xpeedior™ 100 Catheter by Possis, and the Thrombex PMT™ system by Edwards Lifesciences.
Thrombectomy devices have gained popularity in recent years as experience with the devices has increased. However, the use of these devices can be cumbersome, time-consuming and expensive. Furthermore, these devices do not capture emboli in the blood. Rather, these devices are used to remove a thrombus that has formed within a vessel. In certain cases, these devices may actually produce emboli and cause a stroke or PE. Still further, the contact surfaces or fluid pressures of these mechanical thrombectomy devices may produce a variety of undesirable side-effects, such as endothelial denudation and hemolysis. Finally, these devices have not yet proven to be sufficiently mechanically reliable for widespread use.
Therefore, due to the numerous shortcomings associated with existing vascular filters and thrombectomy devices, an urgent need exists for improved devices and methods for capturing and removing blood clots from a patient's vasculature. The present invention addresses this need.